New toilet with poor flush - Metro syphon

[JayJay1978]

We've just had a Wickes bathroom suite installed (supplied by myself) and the toilet has a weak flush and only seems to empty half the cistern.

The toilet is a traditional syphon, flush lever external overflow setup with a short 'Metro' syphon. The syphon has a hole in it which makes me think a blanking plug should go in it because when I cover it with my finger then it does seem to empty the whole cistern and flush properly.

What is this hole for and how can I solve the problem, it takes 2 flushes most times and the guy who installed it says "you suplied the toilet and I just fitted it".

Would a Fluidmaster flapper valve be recommended, are they any good?

Many thanks for any advice.

 

[TicklyT]

Some syphons are fitted with a short flush facility using a hole in the syphon. Holding the operating lever down raises the diaphragm valve to cover the hole, giving a long flush.

Release the handle when the flush starts, and the diaphragm drops clear of the hole, so you only get a short flush.